Explain two important sources of genetic variation in meiosis. Evolutionarily sp

1. independent assortment of chromosomes
Chromosome can sort differently and exchange different amounts of information. It's a little complicated, but basically chromosomes can line up so that the replicates which were formed during meiosis can get multiple allele configurations. Example: Four chromosomes, two homologous pairs replicate. One from each pair has either recessive or dominant alleles. You can end up with either a recessive-recessive and dominant-dominant, or both heterozygous. The sources has a link to help understand more.
2. crossing over
This one is easy, during crossing over with gamete formation, genetic material from the mother (eggs) or father (sperm) are not all the same. You may get different combinations of traits from the father or mother. In other words, since a gamete is technically have the DNA from the father, the same half is not always taken from the father's genome.
3. random fertilization
Sperm all have different combinations of the father's DNA due to crossing over. Mix that up with the eggs from the mother which also contain different parts of her DNA, and you have a random chance that a particular sperm with particular traits is going to fertilize a particular egg with a particular trait. In other words, it's hard to get the exact same genes twice when having kids.

Crossing over and independent assortment provide genetic diversity within a species. This is important because without genetic diversity there is very little chance of a species adapting to the ever-changing environmental conditions. Species with low genetic diversity have a high probability of going extinct if the environmental conditions change.